And actually, it's not surprising you don't see one very often given that a) Ultra High Definition panels are still exceptionally rare, and b) the Sony KD-84X9005 we're gawping at here costs £25,000 in the UK, $US24,999.99 in the US, where it's known as the Sony XBR-84X900, or $AU24,999 in Australia under the code KD-84X9000.

It also has to be said that there's currently not exactly a wealth of native Ultra HD content to feed such a high resolution screen; just your digital photos and a handful of online video files, really. But then there can, of course, be no chicken without an egg (or is it the other way round?).

So we have no problem in principle with Sony getting its Ultra HD guns out for the second time in 2012, following the launch of its stupendous VW1000ES projector. Especially because the Sony KD-84X9005 claims to carry state of the art upscaling of your normal HD and even standard definition content, courtesy of a brand new all-Sony chipset dubbed 4K X-Reality Pro.

Sony has been careful, too, to make sure that the KD-84X9005 feels entirely TV-like, rather than like some 'pro' panels. So it's got a built-in Freeview HD tuner, ships with a pair of bolt-on and startlingly powerful speakers, supports 3D playback, and even carries the new Sony Entertainment Network 'smart TV' online system.

If you'd prefer something similar but different, you could always just scrape together £17,000/AU$25,000/US$25,000 instead for Sony's VW1000ES Ultra HD projector.

Or failing that, £7,000 (around AU$10,850/US$11,208) will get you Toshiba's Ultra HD 55-inch TV, the Toshiba 55ZL2. But as well as producing pictures far smaller than those of the Sony KD-84X9005, Toshiba's TV also provides no way of getting 4K/Ultra High Definition video into it, and features a highly flawed glasses-free 3D TV system.

While only football agents and Russian oligarchs might actually be able to buy a Sony KD-84X9005, though, its Ultra HD capabilities must still be of interest to anyone with even a passing fascination with AV. Especially as they might just provide us an early glimpse of a higher-resolution future. So without further ado, let's get stuck in.

Features

Before sinking our teeth into the 84-inch Sony KD-84X9005's main attractions, let's quickly spare a thought for its design. At first glance this looks a little industrial with its severe black bezel and the slightly clumsy way the full-height speakers bolt on to the screen's sides.

However, the ever-so-shiny finish of the twin-necked floorstand and the unusual ridging that's been applied to the bezel both give the TV an expensive-looking lustre, and the design strangely grows on you over time. Especially if you can place it in a suitably opulent setting.

The main reason for wishing you could afford to spend this huge amount of cash on a TV, though, is obviously the Sony KD-84X9005's native '4K' pixel count. Actually, Ultra HD is a slight exaggeration, since unlike the genuine 4K (4096 x 2160) resolution of the Digital Cinema-aping VW1000ES projector, the Sony KD-84X9005 provides 3840 x 2160 pixels.

This could lead to some interesting aspect ratio discussions, but the main thing is that the Sony KD-84X9005 still presents pictures with comfortably more than eight million pixels in them versus just over two million pixels in normal Full HD images.

Anyone with any interest in picture quality will immediately appreciate the potential impact so many extra pixels could have - especially on a TV screen as gloriously big as 84-inches.

Obviously an Ultra HD screen is always going to look its humdinging best with native 4K sources - as will be underlined during the performance section of this review. So it's an issue that, at the time of writing, native 4K sources are essentially restricted to digital photographs, a handful of short online videos, and the sort of manufacturer demo reels that Sony provided via PC server for this review.

However, the Sony KD-84X9005 does at least cater for native Ultra HD video if and when it does appear via two of its four HDMI inputs - which is more than can be said of the also native Ultra HD Toshiba 55ZL2.

Even more importantly, at least in the short term, the Sony KD-84X9005 features a brand new upscaling chipset designed by Sony specifically for its new 'hero' TV.

Dubbed 4K X-Reality Pro, this new video processing engine combines the frankly scary processing power required to calculate the huge amount of pixels in an Ultra HD picture with Sony's unique 'database' approach. Here the burden on the processing engine is alleviated by the chipset being able to identify a wide array of different video source 'types' to apply pre-determined processing algorithms to.

Of course, Sony also provides a 4K/Ultra High Definition upscaling chipset in its BDP-S790 Blu-ray player.

But it's quick to stress that the one inside the Sony KD-84X9005 is far more sophisticated, advanced and specialised than the one in the BDP-S790 - not least because of the extra demands associated with getting upscaled Ultra HD pictures to look brilliant on a super-large screen.

It's good, too, to discover that Sony has provided a tool set on the Sony KD-84X9005 for adjusting various parameters of its processing engine. For instance, you can tweak the extent to which it adds sharpness to images, and the extent to which the system filters out noise at source.

As we'll see in the performance section of our review, some of these fine tuning touches really are very useful.

Intriguingly considering it's Sony's flagship 2012 TV, the Sony KD-84X9005 is the first TV set from the Japanese brand that uses a passive 3D system rather than an active one. But this isn't as strange a decision as it perhaps initially appears.

Because having double the native horizontal resolution in the Sony KD-84X9005's screen means that for the first time you can enjoy passive 3D with a true Full HD resolution when watching 3D Blu-rays.

There's none of the resolution 'halving' you normally have to put up with, so hopefully you won't see such traditional passive 3D problems as jagged edges, black horizontal lines over bright image content, or a generally slightly rough finish.

If this proves to be the case, then you will hopefully also be able to enjoy all the more vividly passive 3D's notable advantages over its active 3D counterpart: no flickering, practically no crosstalk, and a generally less fatiguing experience.

We'd hoped Sony might also have embraced the cheapness of passive 3D glasses, but bizarrely, despite the Sony KD-84X9005's huge price tag, you only get two pairs included for free. Just as well you can pick up others for pennies.

Despite its huge price and Ultra HD capabilities, Sony believes it's extremely important to sell the Sony KD-84X9005 as a fully fledged TV rather than a mere display. With this in mind, the TV set ships with a built-in Freeview HD tuner, as well as all the normal AV inputs.

There are also USB ports for video, photo and music multimedia playback - something that's particularly significant where JPEG photos are concerned, since for many people their digital photos will be the only way they can immediately experience true 4K images on the Sony KD-84X9005.

Please note that there's a 4K photo option in the menus that you need to check is activated if you want to experience the full resolution monty.

The Sony KD-84X9005 also supports Wi-Fi, with which you can - just as with Sony's 'normal' TVs - stream material from a Mac or DLNA PC via Sony's free HomeStream software. Plus you can go online with the Sony Entertainment Network, which gives you access to an impressive range of services, mostly focused - entirely sensibly - on video streaming.

Wrapping up the Sony KD-84X9005's key features are its use of Sony's most potent MotionFlow XR800 motion processing system, and speakers designed to thrash the puny audio efforts of most flat TVs into a bloody pulp.

These huge speakers run the full height of the TV, and churn out a substantial 50W of audio power from 10 separate drivers, including tweeters, dedicated mid-range units and four subwoofers.

Remember the first time you saw High Definition? Prepare to be amazed again when you experience 4K resolution TV. You'll see everything on a 214cm / 84 inch screen that displays over 8 million pixels in four times more detail than Full HD TV.

Real life detail from only 1.6 metres

Re-create the immersive cinema experience in your home with a huge 214cm / 84 inch 4K resolution widescreen TV, displaying over 8 million individual pixels. Even as close as 1.6m, it's like watching pictures with detail and resolution true to real life.